I have a friend who, years ago, used to go about inserting subtly absurd photos into Wikipedia articles.

One that I recall was for the Refrigerator entry, which he seemingly innocently updated with a "better quality photo" of his own fridge.

If you examined the photo you'd spot that there was a guitar on one of the shelves[1]

[1] http://en.wikipedia.org/w/index.php?title=Refrigerator&oldid...